The invention relates to a method for performing a separating analysis, particularly a quick continuous liquid chromatographic analysis, where the sample is dosed into a separating device and signals corresponding to the concentration of the individual components of the sample are detected by a sensor within certain time intervals. The invention also relates to an arrangement for execution of this method.
Separating analysis are rather unsuitable if components of analyzed mixtures have to be separated and determined continuously and/or within a wide range of mutual concentration ratios and are ineffective, if the overall concentration of the sample is as to its order equal or even lower than the sensitivity of the sensor. As example of a similar analysis there can be mentioned the modern method of liquid chromatography.
Classical methods of liquid chromatography have not found more extensive application, compared to other analytical methods. Only the introduction of sensitive detectors, of modern filter columns and particularly the introduction in use of pressures up to hundreds of atmospheres have brought a number of important advantages resulting in the creation of an entirely new instrumental manufacturing branch of continuous quick pressure liquid chromatography devices. A number of manufacturers have started manufacture of special arrangements and the method is more and more widely applied. This method has however in addition to its advantages also a number of drawbacks. The high pressures require the use of pumps, delivering a constant not pulsating pressure. The design of similar pumps and pressure shock absorbers is not easy; it is expensive and residual pressure variations increase the noise of all known detectors. There are problems furthermore due to the influence of temperatures and occasional troubles due to variations of the resistance which the columns offer to the throughflowing medium. Finally, the discontinuity of the analysis does not permit in a simple manner the creation of continuous processes. An important drawback lies also in the circumstance, that the sensors do not ideally have linear characteristics and are not sensitive within a wide range of concentrations. Further, while the sensors determine well either major or minor components of the analyzed mixture, they never determine with accuracy both simultaneously, but only inaccurately determine the concentration ratio of these components. Also the influence of other kinds of noise for instance of a thermal noise in addition to the required signal reduces the accuracy and sensitivity of the analysis and cannot be eliminated with a large number of repeated analysis.
A method for continuous separating analysis is described in the British patent specification No. 1,036,624 in which an example of a quick continuous liquid chromatographic analysis is described. According to this method the sample is dosed repeatedly in a concentration which is periodically varied with the same number of frequences as analyzed components are supposed to exist. A further supposition is a variable flow speed of the liquid. A synchronous detection is used for each component and therefore also for each frequency, and a mathematical analysis of the proposed method is also provided. The arrangement for execution of this method is practically so complicated and therefore also expensive, that the operation of the arrangement is in practice limited to several analyzed components only and the accuracy of the results is reduced. It is probably for these reasons that this solution has not been applied in practice according to available sources.